Communications systems employ suitable modulated communications media to transfer information from one device to another. An example of which can be light based communications such as employed in infra-red data communications standards to enable devices to communicate with each other. Communications security furthermore is an important part of many communications systems. Securing communications can be achieved in many circumstances by the sharing of cryptographic data such as cryptographic keys which can then be used to encrypt data and secure the means of communications. However, securely sharing the cryptographic data in such a manner that it is difficult to intercept is itself problematic. Although there are known public key systems, it is believed that these systems may not be totally secure and could lead to communications being intercepted, monitored and attacked.